Exhaust gas recirculation control system for internal combustion engines

ABSTRACT

A vacuum operated valve for controlling recirculation of exhaust gases through an internal combustion engine is actuated by the output of a vacuum regulator having a source vacuum from the intake manifold which it regulates according to the vacuum in the venturi of the carburetor to produce a vacuum output which is an amplification of the venturi vacuum. The amplified output is terminated when the engine choke is operative. A reservoir maintains a vacuum to the vacuum regulator during moderate acceleration and a valve responsive to a minimum vacuum in the intake causes the vacuum regulator to cut off its output and close the recirculation valve during heavy acceleration or loading.

VACUUM RESERVOIR I United States Patent 1 1 [111 3,884,200

Caldwell May 20, 1975 [54] EXHAUST GAS RECIRCULATION 3,648,672 3/1972Muroki et a1. 123/119 A CONTROL SYSTEM FOR INTERNAL 3,713,428 l/l973Sandhagen 123/119 A COMBUSTION ENGINES FOREIGN PATENTS OR APPLICATIONS[75] Inventor; Roland B, Caldwell, Columbus 1,601,374 4/1970 Germany123/119 A Ohio Primary ExaminerWendell E. Burns [73] Asslgnee' gilIncorporated Columbus Attorney, Agent, or FirmWatts, Hoffman, Fisher &

Heinke [22] Filed: Aug. 3, 1971 21 Appl. No.: 168,595 [57] ABSTRACT Avacuum operated valve for controlling recirculation of exhaust gasesthrough an internal combustion en- [52] US. Cl 123/119 A gins isactuated by the output f a vacuum regulator [51] Int. Cl. F02m 25/06having a source vacuum f the intake manifold [58] Field of Search.123/103, 1 19 A, 127, l 19 DB, which it regulates according to thevacuum in the ven- 123/119 D; 60/278 turi of the carburetor to produce avacuum output which is an amplification of the venturi vacuum. The [56]References Clted amplified output is terminated when the engine chokeUNITED STATES PATENTS is operative. A reservoir maintains a vacuum tothe 2,071,116 9 7 French 123/1 19 A vacuum regulator during moderateacceleration and a 3,021,827 2/1962 Brunner.... 123/127 valve responsiveto a minimum vacuum in the intake 3,507,260 5/1970 Walker 123/119 Acauses the vacuum regulator to cut off its output and 3,542,003 10/1970a o l 19 A close the recirculation valve during heavy acceleration3,542,004 11/1970 Cornelius 60/278 or l di 3,621,825 11/1971 Ojala123/119 A 3,643,640 2/1972 Kraus 123/119 A 29 Claims, 8 Drawmg Figures58 Q/LAWERELIEF) -j VACUUM REGULATOR MANIFOLD PATENTEDHAYZOIQYS3,884,200

SHEET 1 BF 3 III/ 11/ VIJIJJ 52 v -l3 74) flo H I DUMP (RELIEF) 52 VALVEVACUUM REGULATOR CHECK VACUUM i VALVE REsERvo|R 55 i Fl MANIFOLDINVENTOR. ROLAND B. CALDWELL MJM TTORNEYS PAIENIED 3; 884,200

SHEET 2 BF 3 /VV V0 I II// Fl INVENTOR.

G 4 ROLAND B. GALDWEL.

ATTORNEYS PATENTEUHKY'ZOIQYB 3,884,200

SHEET 3 OF 3 FIG? VACUUMB VOLUME OF Q RECRCULATED GAS FIGB W A c ENGINESPEED W INVENTOR.

ROLAND B. CADWELL FIGB BY 1 2w a M ATTOREYS v EXHAUST GAS RECIRCULATIONCONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THEINVENTION It is well known that nitrogen oxides are produced by internalcombustion engines during lean gas mixture conditions and that theproduction of these oxides may be substantially reduced or eliminated byinjecting or recirculating exhaust gases into the intake manifold. Thispractice is referred to as exhaust gas recirculation and is desirablefor reducing emission of nitrogen oxide from engines of automobiles,etc. During idling, high speeds, heavy acceleration or heavy loading ofan internal combustion engine, recirculation of the exhaust gasesadversely affects operation of the engine and furthermore, under suchconditions, a rich fuel mixture is present which does not produce theobjectional nitrogen oxide-It has been proposed heretofore to provide anexhaust recirculating valve operative under various influences torecirculate exhaust gases only during certain engine operatingconditions so as to minimize the discharge of nitrogen oxide into theatmosphere. Examples of such proposals are disclosed in US. Pat. Nos.2,154,417, 2,419,747 and 3,507,260. These proposals are impractical orcostly and have not been generally adopted.

THE PRESENT INVENTION An object of the present invention is theprovision 'of a valve to control recirculation of exhaust gases inaninternal combustion engine, which valve is operated to increase the flowof recirculated exhaust gases in accordance with the velocity of airdrawn into the carburetor during utilization of relatively lean fuelmixtures by the engine and to reduce or stop the flow of recirculatedexhaust gases in response to relatively rich fuel.

vacuum for operating the valve being provided from the intake manifoldof the engine through a vacuum regulator operated in accordance with thevacuum at the venturi of the engine carburetor and which regulator has avacuum output to the valve actuator which is an amplification of theventuri vacuum. By this arrangement a vacuum for opening the exhaustrecirculating valve is available for increasing the valve opening as therate or volume of combustion air intake of the engine increases within agiven range, and when the intake manifold vacuum decreases below a givenvalue in response to acceleration, loading or high speed, the valve willbe operated to throttle or close off the recirculation of exhaust gases,irrespective of an increase in vacuum at the venturi. i

A further object of the invention is the provision of a vacuum operatedvalve of the character described having means to prevent opening of thevalve during the time the engine choke valve is closed and the vacuum atthe venturi thereby increased beyond normal. A still further object ofthe invention is the provision of a vacuum operated valve of the typedescribed in which the source of operating vacuum for the recirculatingcontrol valve includes a vacuum reservoir to maintain sufficient vacuumto open the valve during moderate acceleration, and valve means to ventthe reservoir in response to a full ope'n throttle condition to preventopening of the recirculating control valve.

Other objects and advantages of the invention will be apparent from thefollowing description of a preferred form of the invention, referencebeing made to the accompanying drawings wherein:

FIG. 1 is a schematic showing of a valve and its controlling componentsfor'controlling the recirculation of exhaust gases through an internalcombustion engine in accordance with the present invention;

FIG. 2 is a sectional view of the exhaust recirculating valve in FIG. 1and shown on a larger scale;

FIG. 3 is a view, partly in section, of a vacuum regulator depicted inFIG. 1 and on a larger scale;

FIG. 4 is a graph depicting the relative vacuum in certain portions ofthe control system and engine for the recirculating valve shown in FIG.1 during different engine speeds;

FIG. 5 is a sectional view of a dump valve shown in FIG. 1 and on alarger scale;

FIGS. 6 and 7 are fragmentary sectional views of the intake of theengine carburetor showingdetails of a choke valve operated in twodifferent positions; and

.FIG. 8 is a graph showing the flow of exhaust gases through therecirculation valve in relation to vacuum conditions in the engine andvalve control system.

Referring to FIG. 1 of the drawings, an exhaust gas recirculating valveand its control system is shown for a four-cycle internal combustionengine for an automotive vehicle. The engine and vehicle are not shownin l .the venturi 12 in the inlet is distributed through the" manifoldto the engine cylinders in the usual manner.

In accordance with the present invention, a valve 16 controls the flowof exhaust gases from the exhaust manifold 15 to the intake manifold 14for recirculation into the cylinders. The inlet of valve 16 is connectedwith the exhaust manifold through a suitable conduit 1,7, and the outletof the valve is connected with the intake manifold through asuitableconduit 20. The valve 16, details of which may be seen in FIG. 2,

' includes a body 21 comprised of two rigid dish shaped members 22, 23arranged with the edges of the open sides joined with a flexiblediaphragm 24 disposed therebetween. The peripheral edges of thediaphragm 24 are hermetically sealed to the joining edges of the members22, 23 and the diaphragm divides the body into separate upper and lowerchambers 25, 26.

The chamber 26 has an inlet 27 in the bottom wall and an outlet 30 inthe side thereof. A valve seat 31 is formed at the inlet 27 and isadapted to be closed by a poppet valve member 32. The valve member 32 isconnected with the diaphragm 24 by a stem 33 and opens and closes theseat 31 in response to deflections of the diaphragm. I

The valve member 32 is urged to close on seat 31 by a spring 34compressed between the top wall of the chamber 25 and the diaphragm 24.The valve member 32 is moved from the valve seat 31 by a vacuum producedin the chamber 25. More or less of a vacuum is produced in the chamberby the output of a vacuum amplifier 35, which is connected with thechamber through a tube 37 attached to an outlet stem 36.

A plate 38 extends across the chamber 26 and defines an opening whichclosely surrounds the valve stem 33. The chamber 26 is open toatmospheric pressure between the plate 38 and the diaphragm 24 via asuitable port or vent opening 39, as is conventional, to enablecontrolled deflection of the diaphragm 24 by the amplifier 35.

As best seen in FIG. 3, the amplifier comprises a frame formed of tworigid dish shaped members 40, 41 having their open sides attached to oneanother about the edges thereof. A flexible diaphragm 42 is disposedbetween the members 40, 41 with the edges thereof hermetically joinedwith the edges of the open side of the member 40. The diaphragm 42 andmember forms an input vacuum signal chamber 43. A vacuum regulatorassembly 44 is suitably secured in an opening in the bottom wall of themember 41. The vacuum regulator 44 is preferably like that which is thesubject matter of U.S. Pat. No. 3,125,111 and includes a body 45 havinga port 48 connected with the interior of the intake manifold, describedmore fully hereinafter, by a tube 47. A vacuum signal output port 46 isconnected with the stem 36 of the chamber 25 of valve 16 by the tube 37.The degree of vacuum signal at the port 46 is determined by the positionof a plunger 50 of the vacuum regulator 44 and which plunger is attachedto the diaphragm 42. The member 41 has an opening therein to atmosphereso that the position of the plunger 50 will depend upon the degree ofvacuum above the diaphragm 42. The manner in which the vacuum signal atthe outlet port 48 is regulated is explained in the aforementioned US,Pat. No. 3,l25,l l l. The vacuum signal chamber 43 has an outlet in theform of a stem 51 which is connected by a tube 52 with the venturi 12 ofthe carburetor as is explained in greater detail hereinafter. Theamplifier 35 is arranged so that as the vacuum in the venturi of thecarburetor increases, the vacuum at the port 48, referred to as theoutput vacuum, increases correspondingly from a zero value, causing thevalve member 32 to move from the seat 31.

In the form shown, the output vacuum of the amplifier 35 is ten timesthat of the vacuum at the venturi 12. Thus, 0.1 Hg vacuum at the venturiwill result in 1.0 Hg vacuum at the outlet 48, provided that degree ofvacuum is present in the manifold. This ratio of amplification, or anyother ratio desired, is obtained by designing the area of diaphragm 42such that the operating plunger 50 will have sufficient force appliedthereto through the diaphragm action to provide the desiredamplification in the vacuum output.

For a fuller understanding of the manner in which the vacuum poweredvalve 16 is operated, reference is made to FIG. 4. Line MV shows theinches of Hg in the intake manifold according to increasing engine RPMunder a constant load, and line VV shows the venturi vacuum forcorresponding engine speeds. Line AV shows the vacuum output of theamplifier 35, the full portion indicating the actual output and thebroken portion indicating the theoretical output if a higher vacuum werepresent in the manifold.

It will be noted that the vertical line VO indicates the engine speed atwhich it is desired to commence recirculation of exhaust gases. In theform shown, the valve member 32 is caused to open when the vacuum abovethe diaphragm 42 increases to 3" Hg by the loading spring 34. Thisincrease in vacuum corresponds to an increase to 0.3 inches Hg ofventuri vacuum. The degree of vacuum required to open the valve 16 couldbe changed by changing the loading characteristics of the spring 34.

The vacuum source for the vacuum amplifier 35 is the intake manifold 14via a conduit 55, a check valve 56, a reservoir tank 57 and the conduit47. The tank 57 is of sufficient size to maintain a vacuum in the inlet47 of the vacuum amplifier 35 during short periods when the vacuum maybe disrupted in the manifold due to temporary rapid opening of theengine throttle. The check valve 56 between the tank 57 and the intakemanifold closes to prevent the vacuum in the tank 57 from dropping tothe level of that in the intake manifold, during the rapid and temporaryexcessive opening of the engine throttle. The check valve may be of anywell known form and a further disclosure of the details thereof areunnecessary to the understanding of the invention.

In the present form of the invention, it is desirable to preventrecirculation of exhaust gases whenever the manifold pressure dropsbelow 3 inches Hg. This condition will occur when the throttle isrelatively fully opened causing a richer fuel mixture to be fed to theengine. Open throttling will occur on heavy accelleration, loading onthe engine or attainment of a high speed of the vehicle driven by theengine. Accordingly, a dump valve 58 is provided between the manifoldand the vacuum signal conduit 52 which opens the signal to atmosphere inresponse to a manifold vacuum of 3 inches or less. Thus, the vacuumoutput of the amplifier 35 is reduced to zero by the dump valve 58whenever the throttle is operated to produce loading of the engine,etc., causing vacuum in the intake manifold to fall below 3 inches Hg.Referring to FIG. 5, the valve 58 comprises a housing formed by theconcave formed members 60, 61 which are joined about the edges of theiropen sides. A diaphragm 62 is crimped between or otherwise hermeticallysecured to, the joined edges of the members 60, 61 and forms with thosemembers upper and lower chambers 63, 64. The upper chamber 63 is open toatmosphere through a passage 65 and the lower chamber 64 is connectedwith the intake manifold through the conduit 55 connected with aconnector nipple 66. A valve housing 67 is provided over the member 60,and the top wall of the member has a valve port 76 therethrough whichopens inside the housing. The port 70 is adapted to be closed by a valvemember 71 which has a stem 72 attached to the diaphragm 62. Acompression spring 73 between the diaphragm and the bottom wall of themember 61 urges the valve member 71 from the port whenever the vacuum inthe member 61 is reduced to 3 inches Hg. When the vacuum in the member61, (and the manifold) is above 3 inches Hg, the valve 71 closes theport '70. The valve housing is connected by a conduit '74 with theconduit 52. Accordingly, when valve member 71 moves from the port 70,the vacuum signal for regulator 35 is reduced to zero through theopening to atmosphere of the dump valve 58. The vacuum output of theother regulator 35 will be zero and valve 16 will be closed.

When the engine choke valve 11 is positioned to restrict air flowthrough the carburetor intake 10, a vacuum will be produced below thechoke valve and at the venturi 12. To prevent opening of the valve 16 bythe regulator 35 in response to a vacuum created by closing of the choke11, a bleed valve 76 is positioned in the intake upstream of the chokevalve 11 and is connected with the conduit 52. The valve 76 includes aport 77 which is positioned to be closed by the choke valve 11 when thechoke is in its open, inoperative position, as seeen in FIG. 6. When thechoke 11 is closed, as seen in FIG. 7, the port 77 is open to atmosphereand consequently the vacuum signal to the regulator 35 is zero and valve16 will remain closed, although the vacuum at the venturi 12 may beabove 0.3 inches Hg.

When the engine is operating at a speed to create 0.] inch Hg at theventuri 12, and a vacuum of at least 3 inches Hg is present in theintake manifold the amplifier 35 will have a vacuum output of 3 inchesHg. This output will cause the valve 16 to open. As the speed of theengine increases by increased opening of the throttle and in the absenceof an appreciable load in the engine, the venturi vacuum will increaseand the amplifier 35 vacuum output will increase, causing the valve 16to open still further. As the engine approaches a wide open throttlecondition, the intake manifold vacuum will decrease below thetheoretical vacuum output of the amplifier 35. This reduction in vacuumcauses the valve 16 to throttle the flow of gas therethrough. When themanifold vacuum is reduced to 3 inches Hg, the valve 58 vents the inputto the amplifier 35 which results in closing of the gas control valve16.

The foregoing description of the flow of recirculated exhaust gas andthe related vacuum values are shown in FIG. 8. R6 represents the volumeof recirculated gas entering the manifold through the valve 16. MVrepresents the vacuum in the intake manifold and VV represents theventuri vacuum. The output vacuum of the amplifier 35 is represented atAV. The dotted portion of AV represents the theoretical vacuum outputinasmuch as the vacuum available in the intake manifold has decreasedbelow the value called for by the amplifier 35. Thus the vacuumavailable for actuating valve 16 is represented by the lines AB and BC.

I claim:

1. In an internal combustion engine including a carburetor having aventuri throat, an intake manifold, an exhaust gas manifold andstructure defining a passageway between said intake and exhaustmanifolds: exhaust gas recirculating valve means effective to controlthe flow of exhaust gas through said passageway, said valve meanscomprising structure defining a vacuum chamber and a valving memberoperative in response to changes in vacuum pressure in said chamber tovary the rate of flow of exhaust gas through said passageway, vacuumcontrol means for controllably communicating said vacuum chamber to saidintake manifold said vacuum control means comprising a vacuum regulatorhaving a vacuum inlet communicating with said intake manifold, aregulated vacuum outlet communicating with said vacuum chamber and apressure signal inlet, and a pressure signal passage between saidventuri throat and said pressure signal inlet, said regulator meanscontrollably communicating said intake manifold and said vacuum chamberin relation to the pressure signal level communicated from said venturithroat to said pressure signal inlet.

2. An internal combustion engine as defined in claim 1 wherein saidvacuum regulator further comprises pressure responsive actuating meanscommunicating with said pressure signal from said venturi throat and 5effective to govern communication between said vacuum inlet and saidvacuum outlet as a function of the vacuum at said venturi throat.

3. An internal combustion engine as defined in claim 2 furthercharacterized by a control valve actuatable to communicate the pressureresponsive actuating means to atmosphere in response to a relativelywide open throttle condition of the engine.

4. An internal combustion engine as defined in claim 2 furthercharacterized by a control valve for communicating the pressure responseactuating means to atmosphere in response to a predetermined vacuum insaid intake manifold.

5. An internal combustion engine as defined in claim 1 wherein saidcarburetor further comprises a choke movement of said choke valve meansto render said vacuum regulator ineffective to respond to the pressuresignal level from said venturi throat.

6. In an internal combustion engine defining at least one combustionchamber, a combustion air intake passage, an exhaust gas passage, and apassageway for communicating said intake and exhaust passages to enablea flow of exhaust gas to said combustion chamber: a fluid pressureoperated valve means for controlling the flow of exhaust gas via saidpassageway into said combustion chamber, said valve means operablebetween an open condition and a closed condition wherein the flow ofexhaust gas through said passageway is substantially terminated, fluidpressure source means providing a supply of fluid pressure communicablewith said valve means for operating said valve means, a fluid pressureregulator adapted to control the fluid pressure communication betweensaid source and said valve means for governing operation of said valvemeans between said conditions, and regulator controlling signal meansfor supplying fluid input signal to said regulator which varies as afunction of the rate of flow of gas through the engine, said regulatoreffective to govern communication between said source and said valvemeans in response to said fluid input signal.

7. An internal combustion engine defined in claim 6 in which said fluidpressure source means comprises the intake manifold to said engine, andsaid regulator controlling signal means comprises a venturi in said airintake. I

8. An internal combustion engine as defined in claim 7 furthercharacterized by means responsive to a relatively wide open throttlecondition of said engine for operating said valve means to the closedcondition.

9. An internal combustion engine as defined in claim 6 furthercharacterized by means responsive to a drop in manifold vacuum forclosing said valve.

10. An internal combustion engine as defined in claim 7 furthercharacterized by means to supersede the control of said regulator bysaid venturi in response to a given pressure in said intake manifold.

11. In combination with an internal combustion engine having an airintake passage, a throttle means for governing the flow of combustionair entering the engine, and an exhaust passage, a system forintroducing exhaust gas into said intake passage from said exhaustpassage under predetermined running conditions of the valve means, andvalving means responsive to closing engine comprising: a flow passagewaybetween said intake passage and said exhaust passage; differentialpressure responsive valve means comprising a valve member in saidpassageway which is movable in response to differential pressure appliedto said valve means to enable flow through said passageway to vary, saidvalve member having a closed position in which exhaust gas flow throughsaid passageway is blocked; source means communicable with said valvemeans and defining a source of operating pressure for said valve meanswhich varies substantially in relation to operation of the throttlemeans; regulator means connected between said source means and saidvalve means for controlling the magnitude of the source means pressurecommunicated to said valve means to govern the differential pressureapplied to said valve means, said regulator means comprising a regulatormember movable inrelation to changes in the rate of combustion airintake into said engine from a first position at engine intake air flowrates below a predetermined flow rate wherein said valve member is inits closed position, said member moving from said first position inresponse to increasing flow rates of engine intake air above saidpredetermined rate whereby said regulator means is effective to increasedifferential pressure applied to said valve means to progressively movesaid valve member from said closed position; and said souce meanspressure progressively changing as the engine approaches an openthrottle condition to progressively reduce the differential pressureavailable for operating said valve means irrespective of the position ofsaid regulator member so that said regulator means is ineffective togovern the communication between said source means and said valve meanswhen the differential pressure demanded by said regulator means isgreater than the differential pressure available from said source means,the position of said valve member thereafter controlled directly fromsaid source means in relation to changes in source means pressure. I

12. The combination claimed in claim 11 further including means foroperating said regulator member to said first position in response todetection of intake passage static pressures less than a predeterminedrelatively low magnitude with respect to atmospheric pressure so thatsaid valve member is operated to said closed position.

13. The combination claimed in claim 11 further including a choke valvein said intake passage and structure cooperable with said choke valveand said regulator means for effecting movement of said regulator memberto its first position when said choke valve is away from its inoperativeposition whereby said valve member is in its closed position when theengine is choked.

14. A method of controllably recirculating engine exhaust gas into thecombustion intake air of an engine to reduce the production ofundesirable exhaust emissions from the engine comprising:

a. providing a passageway through which engine exhaust gas can flow formixing with intake combustion air; and,

b. valving the flow of engine exhaust gas through the passageway inresponse to engine operating conditions including:

i. providing a pressure operated valve means actuable according to themagnitude of an applied pressure differential to modulate the flow ofrecirculated exhaust gas;

ii. communicating the valve means to a source of valve means operatingfluid pressure;

iii. sensing the rate of flow of intake combustion air to the engine;

iv. controlling the communication of valve means operating fluidpressure from the source as a function of sensed intake combustion airflow rates above a predetermined rate so that said valve means isoperated to enable increased recirculation of exhaust gas as intakecombustion air flow rates increase 'above the predetermined rate; and,

v. reducing the magnitude of the valve means operating source pressureas the engine approaches a wide-open-throttle condition to reduce thevalve means operating pressure applied to the valve means irrespectiveof the sensed intake combustion air flow rate whereby the amount ofrecirculated exhaust gas is reduced as the engine approaches the wideopen throttle condition.

15. The method defined in claim 14 further charac- J terized bymaintaining the valve means operating pressure less than .a givenmagnitude while the sensed flow rate of intake combustion air is lessthan said predetermined rate whereby recirculation of exhaust gas isminimized.

16. The method defined in claim 14 wherein sensing the flow rate ofintake combustion air comprises determining a pressure of the combustionair flowing in-an air intake of the engine and controlling communicationfrom the source to the valve means comprises controlling the magnitudeof the operating pressure applied to the valve means as a function ofthe sensed pressure of the intake air flowing in the engine air intake.

17. The method defined in claim 16 further characterized by maintainingthe operating pressure applied to said valve means at a predeterminedgreater magnitude than the magnitude of the sensed pressure. of the airflowing inthe air intake of the engine throughout a given range ofintake combustion air flow rates and while the source pressure isgreater than the predetermined valve operating pressure magnitude.

18. The method defined in claim 14 further characterized by terminatingsaid flow of recirculating exhaust gas when the magnitude of the sourcepressure is reduced below a given minimum.

19. In an exhaust gas recirculation system for an internal combustionengine having a combustion air intake duct in which a throttle valveislocated, an intake it manifold defined downstream from said throttlevalve, an exhaust manifold and a flow passageway defined between saidexhaust manifold and said intake manifold: a. exhaust gas recirculatingvalve means for enabling exhaust gas from the exhaust manifold to berecirculated to the intake manifold through said flow passageway, saidrecirculating valve means comprising a valve member operated by pressureenergy supplied from said intake manifold and having an open conditionwherein exhaust gas is recirculated and a closed condition forpreventing exhaust gas recirculation, said valve member operable in saidopen condition to modulate the flow of recirculated exhaust gas throughsaid flow passageway;

b. pressure regulator means for controlling the magnitude of thepressure communicated between the recirculating valve means and theintake manifold in relation to the flow rate of air in the combustionair intake duct under predetermined engine operat ing conditions and inrelation to the intake manifold pressure under other predeterminedengine operating conditions;

c. said pressure regulator means defining:

i. an input signal pressure port in communication with said intake ductat a location upstream from said throttle valve for providing intake airflow rate responsive pressure signals to said regulator means,

ii. an input operating pressure port in communication with said intakemanifold; and,

iii. an output valve operating pressure port in communication with saidrecirculating valve means;

d. said regulator means variably communicating valve operating pressureto said valve means as an amplified function of the input signal leveland effective to amplify input pressure signal levels for application tothe recirculating valve means via said valve operating pressure port;

e. said regulator means operative to govern the recirculating valvecondition as a direct function of intake manifold pressure independentlyof the air flow rate in the intake duct when the engine is operatedunder a condition wherein the output valve operating pressure requiredby the input signal level would otherwise exceed the intake manifoldpressure.

20. In an exhaust gas recirculation system for an internal combustionengine having a combustion air intake duct through which combustion airflows to a combustion chamber, a throttle valve disposed in said airduct, an engine exhaust gas system through which exhaust gas flows fromsaid combustion chamber, and passage means defining a flow path alongwhich exhaust gas may flow from said exhaust gas system for mixing withcombustion air:

a. pressure operated valve means for controlling the flow of exhaust gasin said passage means, said valve means comprising a valve member havingan open condition in which the flow of exhaust gas in said passage meansis controlled and a closed condition wherein exhaust gas flow in saidpassage means is blocked;

b, pressure source means defined at least in part by a portion of saidintake duct downstream from said throttle valve;

c. pressure signal means defined at least in part by a second portion ofsaid intake duct upstream from said throttle valve and effective toproduce a pressure signal having a relatively small magnitude and whichvaries in relation to the flow rate of intake air in said second ductportion; and,

d. pressure regulator means for controlling the condition of said valvemeans and defining a signal pressure input port communicating with saidpressure signal means, a pressure source port communicating with saidpressure source means and a valve operating pressure output portcommunicating with said valve means, said regulator means effective tovariably communicate valve operating pressure from said source means tosaid valve means via said output port as an amplified function of inputpressure signals provided to said signal pressure input port forcontrolling operation of said valve means in its open condition as afunction of said input pressure signals under predetermined operatingconditions of the engine, said regulator means directly communicatingsaid valve means to said pressure source means to control operation ofsaid valve means in its open condition as a direct function of saidsource means pressure irrespective of intake air flow rate pressuresignal levels when the output port pressure level demanded by thepressure signal is of greater magnitude than the source means pressure.

21. In an internal combustion engine including a combustion air intake,a fluid pressure operated valve means for controlling the recirculationof exhaust gases into the combustion chambers of said engine, sourcemeans providing a source of fluid pressure connected with said valve foroperating said valve, said source means comprising an intake manifold ofsaid engine, a fluid pressure regulator adapted to regulate the fluidpressure from said source to said valve, means comprising a venturi insaid air intake for controlling said regulator in response to changes invelocity of the air entering the engine through said intake, and meansresponsive to a relatively wide open throttle condition of said enginefor closing said valve means.

22. In an internal combustion engine including a combustion air intake,a fluid pressure operated valve means for controlling the recirculationof exhaust gases into the combustion chambers of said engine, sourcemeans providing a source of fluid pressure connected with said valve foroperating said valve, said source means comprising an intake manifold ofsaid engine, a fluid pressure regulator adapted to regulate the fluidpressure from said source to said valve, means comprising a venturi insaid air intake for controlling said regulator in response to changes invelocity of the air entering the engine through said intake, and meansresponsive to a drop in intake manifold vacuum for closing said valve.

23. In an internal combustion engine including a combustion air intake,a fluid pressure operated valve means for controlling the recirculationof exhaust gases into the combustion chambers of said engine, sourcemeans providing a source of fluid pressure connected with said valve foroperating said valve, said source means comprising an intake manifold ofsaid engine, a fluid pressure regulator adapted to regulate the fluidpressure from said source to said valve, means comprising a venturi insaid air intake for controlling said regulator in response to changes invelocity of the air entering the engine through said intake, and meansto supersede the control of said regulator by said venturi in responseto a given pressure in said intake manifold.

24. In an internal combustion engine including a carburetor having aventuri throat and an intake manifold, valve means to control the flowof exhaust gas to the combustion chambers of said engine, said valvemeans including a vacuum chamber and a member operative in response tochanges in vacuum in said chamber to vary the rate of flow through saidvalve means, characterized by means for connecting said vacuum chamberto said intake manifold whereby the vacuum in said manifold affects thevacuum in said chamber and including a vacuum regulator having a vacuuminlet connected with said intake manifold and a regulated vacuum outletconnected with said vacuum chamber, means to control said vacuumregulator in response to the vacuum at the venturi of said enginecomprising pressure responsive actuating means connected with saidventuri throat and responding to the vacuum at said throat, and a valvefor connecting the pressure responsive actuating means to atmosphere inresponse to a relatively wide open throttle condition of the engine.

25. In an internal combustion engine including a carburetor having aventuri throat and an intake manifold, valve means to control the flowof exhaust gas to the combustion chambers of said engine, said valvemeans including a vacuum chamber and a member operative in response tochanges in vacuum in said chamber to vary the rate of flow through saidvalve means, characterized by means for connecting said vacuum chamberto said intake manifold whereby the vacuum in said manifold affects thevacuum in said chamber and including a vacuum regulator having a vacuuminlet connected with said intake manifold and a regulated vacuum outletconnected with said vacuum chamber, means to control said vacuumregulator in response to the vacuum at the venturi of said enginecomprising pressure responsive actuating means connected with saidventuri throat and responding to the vacuum at said throat, and, a valvefor connecting the pressure responsive actuating means to atmosphere inresponse to a predetermined vacuum in said manifold.

26. In an internal combustion engine including a carburetor having aventuri throat and choke valve means, and an intake manifold, valvemeans to control the flow of exhaust gas to the combustion chambers ofsaid engine, said valve means including a vacuum chamber and a memberoperative in response to changes in vacuum in said chamber to vary therate of flow through said valve means, characterized by means forconnecting said vacuum chamber to said intake manifold whereby thevacuum in said manifold affects the vacuum in said chamber and includinga vacuum regulator having a vacuum inlet connected with said intake manifold and a regulated vacuum outlet connected with said vacuum chamber,means to control said vacuum regulator in response to the vacuum at theventuri of said engine, and means responsive to closing movement of saidchoke valve means to render said vacuum regulator inoperative to actuatesaid valve means controlling flow of gas into said engine.

27. In an internal combustion engine including a carburetor having aventuri throat and an intake manifold, valve means to control the flowof exhaust gas to the combustion chambers of said engine, said valvemeans including a vacuum chamber and a member operative in response tochanges in vacuum in said chamber to vary the rate of flow through saidvalve means, characterized by means for connecting said vacuum chamberto said intake manifold whereby the vacuum in said manifold affects thevacuum in said chamber and including a vacuum regulator having a vacuuminlet connected with said intake manifold and a regulated vacuum outletconnected with said vacuum chamber, and means to control said vacuumregulator in response to the vacuum at the venturi of said engine, saidmeans to control said vacuum regulator being effective to cause theregulator to provide an output of vacuum having an appreciably higherinches of mercury value than the inches of mercury value of the vacuumat the venturi throat.

28. A method of controllably recirculating engine exhaust gas into thecombustion intake air of an engine to reduce the production ofundesirable exhaust emissions from the engine comprising:

a. providing an engine intake combustion air passage, an engine exhaustgas passage, and a passageway through which engine exhaust gas can flowfor mixing with intake combustion air; and,

b. valving the flow of engine exhaust gas through said passageway inresponse to engine operating conditions including:

i. providing a pressure operated valve means actuable to control theflow through said passageway;

ii. communicating said valve means to a source of valve means operatingpressure;

iii. sensing the flow rate in one of said passages;

iv. producing a fluid signal which varies according to the sensed flowrate in said one passage;

v. controlling the communication of valve means operating fluid pressureto said valve means from said source according to said fluid signal tocontrol flow through said passageway; and,

vi. reducing the magnitude of the fluid pressure applied to the valvemeans when the engine is operated substantially at a wide open throttlecondition for operating said valve means to minimize flow through saidpassageway irrespective of the flow rate in said one passage.

29. The method claimed in claim 28 further comprising operating thevalve means to a condition for minimizing flow through said passagewaywhen the engine is operated at idle speed.

1. In an internal combustion engine including a carburetor having aventuri throat, an intake manifold, an exhaust gas manifold andstructure defining a passageway between said intake and exhaustmanifolds: exhaust gas recirculating valve means effective to controlthe flow of exhaust gas through said passageway, said valve meanscomprising structure defining a vacuum chamber and a valving memberoperative in response to changes in vacuum pressure in said chamber tovary the rate of flow of exhaust gas through said passageway, vacuumcontrol means for controllably communicating said vacuum chamber to saidintake manifold said vacuum control means comprising a vacuum regulatorhaving a vacuum inlet communicating with said intake manifold, aregulated vacuum outlet communicating with said vacuum chamber and apressure signal inlet, and a pressure signal passage between saidventuri throat and said pressure signal inlet, said regulator meanscontrollably communicating said intake manifold and said vacuum chamberin relation to the pressure signal level communicated from said venturithroat to said pressure signal inlet.
 2. An internal combustion engineas defined in claim 1 wherein said vacuum regulator further comprisespressure responsive actuating means communicating with said pressuresignal from said venturi throat and effective to govern communicationbetween said vacuum inlet and said vacuum outlet as a function of thevacuum at said venturi throat.
 3. An internal combustion engine asdefined in claim 2 further characterized by a control valve actuatableto communicate the pressure responsive actuating means to atmosphere inresponse to a relatively wide open throttle condition of the engine. 4.An internal combustion engine as defined in claim 2 furthercharacterized by a control valve for communicating the pressure responseactuating means to atmosphere in response to a predetermined vacuum insaid intake manifold.
 5. An internal combustion engine as defined inclaim 1 wherein said carburetor further comprises a choke valve means,and valving means responsive to closing movement of said choke valvemeans to render said vacuum regulator ineffective to respond to thepressure signal level from said venturi throat.
 6. In an internalcombustion engine defining at least one combustion chamber, a combustionair intake passage, an exhaust gas passage, and a passageway forcommunicating said intake and exhaust passages to enable a flow ofexhaust gas to said combustion chamber: a fluid pressure operated valvemeans for controlling the flow of exhaust gas via said passageway intosaid combustion chamber, said valve means operable between an opencondition and a closed condition wherein the flow of exhaust gas throughsaid passageway is substantially terminated, fluid pressure source meansproviding a supply of fluid pressure communicable with said valve meansfor operating said valve means, a fluid pressure regulator adapted tocontrol the fluid pressure communication between said source and saidvalve means for governing operation of said valve means between saidconditions, and regulator controlling signal means for supplying fluidinput signal to said regulator which varies as a function of the rate offlow of gas through the engine, said regulator effective to governcommunication between said source and said valve means in response tosaid fluid input signal.
 7. An internal combustion engine defined inclaim 6 in which said fluid pressure source means comprises the intakemanifold to said engine, and said regulator controlling signal meanscomprises a venturi in said air intake.
 8. An internal combustion engineas defined in claim 7 further characterized by means responsive to arelatively wide open throttle condition of said engine for operatingsaid valve means to the closed condition.
 9. An internal combustionengine as defined in claim 6 further characterized by means responsiveto a drop in manifold vacuum for closing said valve.
 10. An internalcombustion engine as defined in claim 7 further characterized by meansto supersede the control of said regulator by said venturi in responseto a given pressure in said intake manifold.
 11. In combination with aninternal combustion engine having an air intake passage, a throttlemeans for governing the flow of combustion air entering the engine, andan exhaust passage, a system for introducing exhaust gas into saidintake passage from said exhaust passage under predetermined runningconditions of the engine comprising: a flow passageway between saidintake passage and said exhaust passage; differential pressureresponsive valve means comprising a valve member in said passagewaywhich is movable in response to differential pressure applied to saidvalve means to enable flow through said passageway to vary, said valvemember having a closed position in which exhaust gas flow through saidpassageway is blocked; source means communicable with said valve meansand defining a source of operating pressure for said valve means whichvaries substantially in relation to operation of the throttle means;regulator means connected between said source means and said valve meansfor controlling the magnitude of the source means pressure communicatedto said valve means to govern the differential pressure applied to saidvalve means, said regulator means comprising a regulator member movablein relation to changes in the rate of combustion air intake into saidengine from a first position at engine intake air flow rates below apredetermined flow rate wherein said valve member is in its closedposition, said member moving from said first position in response toincreasing flow rates of engine intake air above said predetermined ratewhereby said regulator means is effective to increase differentialpressure applied to said valve means to progressively move said valvemember from said closed position; and said souce means pressureprogressively changing as the engine approaches an open throttlecondition to progressively reduce the differential pressure availablefor operating said valve means irrespective of the position of saidregulator member so that said regulator means is ineffective to governthe communication between said source means and said valve means whenthe differential pressure demanded by said regulator means is greaterthan the differential pressure available from saiD source means, theposition of said valve member thereafter controlled directly from saidsource means in relation to changes in source means pressure.
 12. Thecombination claimed in claim 11 further including means for operatingsaid regulator member to said first position in response to detection ofintake passage static pressures less than a predetermined relatively lowmagnitude with respect to atmospheric pressure so that said valve memberis operated to said closed position.
 13. The combination claimed inclaim 11 further including a choke valve in said intake passage andstructure cooperable with said choke valve and said regulator means foreffecting movement of said regulator member to its first position whensaid choke valve is away from its inoperative position whereby saidvalve member is in its closed position when the engine is choked.
 14. Amethod of controllably recirculating engine exhaust gas into thecombustion intake air of an engine to reduce the production ofundesirable exhaust emissions from the engine comprising: a. providing apassageway through which engine exhaust gas can flow for mixing withintake combustion air; and, b. valving the flow of engine exhaust gasthrough the passageway in response to engine operating conditionsincluding: i. providing a pressure operated valve means actuableaccording to the magnitude of an applied pressure differential tomodulate the flow of recirculated exhaust gas; ii. communicating thevalve means to a source of valve means operating fluid pressure; iii.sensing the rate of flow of intake combustion air to the engine; iv.controlling the communication of valve means operating fluid pressurefrom the source as a function of sensed intake combustion air flow ratesabove a predetermined rate so that said valve means is operated toenable increased recirculation of exhaust gas as intake combustion airflow rates increase above the predetermined rate; and, v. reducing themagnitude of the valve means operating source pressure as the engineapproaches a wide-open-throttle condition to reduce the valve meansoperating pressure applied to the valve means irrespective of the sensedintake combustion air flow rate whereby the amount of recirculatedexhaust gas is reduced as the engine approaches the wide open throttlecondition.
 15. The method defined in claim 14 further characterized bymaintaining the valve means operating pressure less than a givenmagnitude while the sensed flow rate of intake combustion air is lessthan said predetermined rate whereby recirculation of exhaust gas isminimized.
 16. The method defined in claim 14 wherein sensing the flowrate of intake combustion air comprises determining a pressure of thecombustion air flowing in an air intake of the engine and controllingcommunication from the source to the valve means comprises controllingthe magnitude of the operating pressure applied to the valve means as afunction of the sensed pressure of the intake air flowing in the engineair intake.
 17. The method defined in claim 16 further characterized bymaintaining the operating pressure applied to said valve means at apredetermined greater magnitude than the magnitude of the sensedpressure of the air flowing in the air intake of the engine throughout agiven range of intake combustion air flow rates and while the sourcepressure is greater than the predetermined valve operating pressuremagnitude.
 18. The method defined in claim 14 further characterized byterminating said flow of recirculating exhaust gas when the magnitude ofthe source pressure is reduced below a given minimum.
 19. In an exhaustgas recirculation system for an internal combustion engine having acombustion air intake duct in which a throttle valve is located, anintake manifold defined downstream from said throttle valve, an exhaustmanifold and a flow passageway defined between said exhaust manifold andsaid intake manifold: a. exhaust gas recircuLating valve means forenabling exhaust gas from the exhaust manifold to be recirculated to theintake manifold through said flow passageway, said recirculating valvemeans comprising a valve member operated by pressure energy suppliedfrom said intake manifold and having an open condition wherein exhaustgas is recirculated and a closed condition for preventing exhaust gasrecirculation, said valve member operable in said open condition tomodulate the flow of recirculated exhaust gas through said flowpassageway; b. pressure regulator means for controlling the magnitude ofthe pressure communicated between the recirculating valve means and theintake manifold in relation to the flow rate of air in the combustionair intake duct under predetermined engine operating conditions and inrelation to the intake manifold pressure under other predeterminedengine operating conditions; c. said pressure regulator means defining:i. an input signal pressure port in communication with said intake ductat a location upstream from said throttle valve for providing intake airflow rate responsive pressure signals to said regulator means; ii. aninput operating pressure port in communication with said intakemanifold; and, iii. an output valve operating pressure port incommunication with said recirculating valve means; d. said regulatormeans variably communicating valve operating pressure to said valvemeans as an amplified function of the input signal level and effectiveto amplify input pressure signal levels for application to therecirculating valve means via said valve operating pressure port; e.said regulator means operative to govern the recirculating valvecondition as a direct function of intake manifold pressure independentlyof the air flow rate in the intake duct when the engine is operatedunder a condition wherein the output valve operating pressure requiredby the input signal level would otherwise exceed the intake manifoldpressure.
 20. In an exhaust gas recirculation system for an internalcombustion engine having a combustion air intake duct through whichcombustion air flows to a combustion chamber, a throttle valve disposedin said air duct, an engine exhaust gas system through which exhaust gasflows from said combustion chamber, and passage means defining a flowpath along which exhaust gas may flow from said exhaust gas system formixing with combustion air: a. pressure operated valve means forcontrolling the flow of exhaust gas in said passage means, said valvemeans comprising a valve member having an open condition in which theflow of exhaust gas in said passage means is controlled and a closedcondition wherein exhaust gas flow in said passage means is blocked; b.pressure source means defined at least in part by a portion of saidintake duct downstream from said throttle valve; c. pressure signalmeans defined at least in part by a second portion of said intake ductupstream from said throttle valve and effective to produce a pressuresignal having a relatively small magnitude and which varies in relationto the flow rate of intake air in said second duct portion; and, d.pressure regulator means for controlling the condition of said valvemeans and defining a signal pressure input port communicating with saidpressure signal means, a pressure source port communicating with saidpressure source means and a valve operating pressure output portcommunicating with said valve means, said regulator means effective tovariably communicate valve operating pressure from said source means tosaid valve means via said output port as an amplified function of inputpressure signals provided to said signal pressure input port forcontrolling operation of said valve means in its open condition as afunction of said input pressure signals under predetermined operatingconditions of the engine, said regulator means directly communicatingsaid valve means to said pressure source means to control operation ofsaid valve meaNs in its open condition as a direct function of saidsource means pressure irrespective of intake air flow rate pressuresignal levels when the output port pressure level demanded by thepressure signal is of greater magnitude than the source means pressure.21. In an internal combustion engine including a combustion air intake,a fluid pressure operated valve means for controlling the recirculationof exhaust gases into the combustion chambers of said engine, sourcemeans providing a source of fluid pressure connected with said valve foroperating said valve, said source means comprising an intake manifold ofsaid engine, a fluid pressure regulator adapted to regulate the fluidpressure from said source to said valve, means comprising a venturi insaid air intake for controlling said regulator in response to changes invelocity of the air entering the engine through said intake, and meansresponsive to a relatively wide open throttle condition of said enginefor closing said valve means.
 22. In an internal combustion engineincluding a combustion air intake, a fluid pressure operated valve meansfor controlling the recirculation of exhaust gases into the combustionchambers of said engine, source means providing a source of fluidpressure connected with said valve for operating said valve, said sourcemeans comprising an intake manifold of said engine, a fluid pressureregulator adapted to regulate the fluid pressure from said source tosaid valve, means comprising a venturi in said air intake forcontrolling said regulator in response to changes in velocity of the airentering the engine through said intake, and means responsive to a dropin intake manifold vacuum for closing said valve.
 23. In an internalcombustion engine including a combustion air intake, a fluid pressureoperated valve means for controlling the recirculation of exhaust gasesinto the combustion chambers of said engine, source means providing asource of fluid pressure connected with said valve for operating saidvalve, said source means comprising an intake manifold of said engine, afluid pressure regulator adapted to regulate the fluid pressure fromsaid source to said valve, means comprising a venturi in said air intakefor controlling said regulator in response to changes in velocity of theair entering the engine through said intake, and means to supersede thecontrol of said regulator by said venturi in response to a givenpressure in said intake manifold.
 24. In an internal combustion engineincluding a carburetor having a venturi throat and an intake manifold,valve means to control the flow of exhaust gas to the combustionchambers of said engine, said valve means including a vacuum chamber anda member operative in response to changes in vacuum in said chamber tovary the rate of flow through said valve means, characterized by meansfor connecting said vacuum chamber to said intake manifold whereby thevacuum in said manifold affects the vacuum in said chamber and includinga vacuum regulator having a vacuum inlet connected with said intakemanifold and a regulated vacuum outlet connected with said vacuumchamber, means to control said vacuum regulator in response to thevacuum at the venturi of said engine comprising pressure responsiveactuating means connected with said venturi throat and responding to thevacuum at said throat, and a valve for connecting the pressureresponsive actuating means to atmosphere in response to a relativelywide open throttle condition of the engine.
 25. In an internalcombustion engine including a carburetor having a venturi throat and anintake manifold, valve means to control the flow of exhaust gas to thecombustion chambers of said engine, said valve means including a vacuumchamber and a member operative in response to changes in vacuum in saidchamber to vary the rate of flow through said valve means, characterizedby means for connecting said vacuum chamber to said intake manifoldwhereby the vacuum in said manifold affects the vacuum in said chamberand including a vacuum regulator having a vacuum inlet connected withsaid intake manifold and a regulated vacuum outlet connected with saidvacuum chamber, means to control said vacuum regulator in response tothe vacuum at the venturi of said engine comprising pressure responsiveactuating means connected with said venturi throat and responding to thevacuum at said throat, and, a valve for connecting the pressureresponsive actuating means to atmosphere in response to a predeterminedvacuum in said manifold.
 26. In an internal combustion engine includinga carburetor having a venturi throat and choke valve means, and anintake manifold, valve means to control the flow of exhaust gas to thecombustion chambers of said engine, said valve means including a vacuumchamber and a member operative in response to changes in vacuum in saidchamber to vary the rate of flow through said valve means, characterizedby means for connecting said vacuum chamber to said intake manifoldwhereby the vacuum in said manifold affects the vacuum in said chamberand including a vacuum regulator having a vacuum inlet connected withsaid intake manifold and a regulated vacuum outlet connected with saidvacuum chamber, means to control said vacuum regulator in response tothe vacuum at the venturi of said engine, and means responsive toclosing movement of said choke valve means to render said vacuumregulator inoperative to actuate said valve means controlling flow ofgas into said engine.
 27. In an internal combustion engine including acarburetor having a venturi throat and an intake manifold, valve meansto control the flow of exhaust gas to the combustion chambers of saidengine, said valve means including a vacuum chamber and a memberoperative in response to changes in vacuum in said chamber to vary therate of flow through said valve means, characterized by means forconnecting said vacuum chamber to said intake manifold whereby thevacuum in said manifold affects the vacuum in said chamber and includinga vacuum regulator having a vacuum inlet connected with said intakemanifold and a regulated vacuum outlet connected with said vacuumchamber, and means to control said vacuum regulator in response to thevacuum at the venturi of said engine, said means to control said vacuumregulator being effective to cause the regulator to provide an output ofvacuum having an appreciably higher inches of mercury value than theinches of mercury value of the vacuum at the venturi throat.
 28. Amethod of controllably recirculating engine exhaust gas into thecombustion intake air of an engine to reduce the production ofundesirable exhaust emissions from the engine comprising: a. providingan engine intake combustion air passage, an engine exhaust gas passage,and a passageway through which engine exhaust gas can flow for mixingwith intake combustion air; and, b. valving the flow of engine exhaustgas through said passageway in response to engine operating conditionsincluding: i. providing a pressure operated valve means actuable tocontrol the flow through said passageway; ii. communicating said valvemeans to a source of valve means operating pressure; iii. sensing theflow rate in one of said passages; iv. producing a fluid signal whichvaries according to the sensed flow rate in said one passage; v.controlling the communication of valve means operating fluid pressure tosaid valve means from said source according to said fluid signal tocontrol flow through said passageway; and, vi. reducing the magnitude ofthe fluid pressure applied to the valve means when the engine isoperated substantially at a wide open throttle condition for operatingsaid valve means to minimize flow through said passageway irrespectiveof the flow rate in said one passage.
 29. The method claimed in claim 28further comprising operating the valve means to a condition forminimizing flow through said passageway when the engine is operated atidlE speed.